Recent studies have demonstrated that patients with cholesterol gallstones have a bile salt pool size that is small in comparison to normal individuals. Other investigators have suggested that expansion of the bile salt pool by long-term administration of the bile salt, che- nodeoxycholic acid, can produce dissolution of established cholesterol cholelithiasis. The principal investigator of this proposed grant has established that baboons are the ideal - and only - animal model that is relevant for the investigation of human cholesterol gallstone formation. It is the purpose of this study to evaluate the biologic and toxic effects of chronic chenodeoxycholate administration to female baboons. Specifically, the parameters to be evaluated include biliary tract, hepatic, cardiovascular and reproductive functions. Biliary tract and hepatic function will be monitored to detect evidence of cell injury and defects in metabolic and excretory function. Cellular function will be monitored by measurement of SGOT, SGPT and 5'nucleotidase as well as serial liver biopsy. Metabolic and excretory function will be by measurement of prothombin time, serum albumin and bile salt levels and BSP disappearance curve. The effects of chronic bile salt administration on the cardiovascular system will be evaluated by measurement of changes in the cholesterol pool size and quantitative measurement of atheromatous changes in the cardiovascular system by autopsy at the termination of the study. The changes in reproductive function to be monitored include the effects on menstruation, fertility and fetal maturation.